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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 3 | Copyright

Special issue: Drought forecasting and warning

Hydrol. Earth Syst. Sci., 18, 1239-1249, 2014
https://doi.org/10.5194/hess-18-1239-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 31 Mar 2014

Research article | 31 Mar 2014

Droughts and floods over the upper catchment of the Blue Nile and their connections to the timing of El Niño and La Niña events

M. A. H. Zaroug1,2, E. A. B. Eltahir3, and F. Giorgi1 M. A. H. Zaroug et al.
  • 1International Center for Theoretical Physics, Earth System Physics, Trieste, Italy
  • 2Dinder Center for Environmental Research, Khartoum, Sudan
  • 3Massachusetts Institute of Technology, Civil and Environmental Engineering, Cambridge, USA

Abstract. The Blue Nile originates from Lake Tana in the Ethiopian Highlands and contributes about 60–69% of the main Nile discharge. Previous studies investigated the relationship of sea surface temperature (SST) in the Pacific Ocean (Niño 3.4 region) to occurrence of meteorological and hydrological droughts in the Nile Basin. In this paper we focus on the dependence of occurrence of droughts and floods in the upper catchment of the Blue Nile on the timing of El Niño and La Niña events. Different events start at different times of the year and follow each other, exhibiting different patterns and sequences. Here we study the impact of these timing and temporal patterns on the Blue Nile droughts and floods. The comparison between the discharge measurements (1965–2012) at the outlet of the upper catchment of the Blue Nile and the El Niño index shows that when an El Niño event is followed by a La Niña event, there is a 67% chance for occurrence of an extreme flood. Furthermore, we also found that 83% of El Niño events starting in April–June resulted in droughts in the upper catchment of the Blue Nile. Although the current study is limited by the reduced number of samples, we propose that observations as well as global model forecasts of SST during this season could be used in seasonal forecasting of the Blue Nile flow.

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